rate of reaction

Two compounds X and Y react to produce compound Z. The reaction is reversible.

X + Y → Z

When X and Y are mixed together in a closed system a dynamic equilibrium is gradually

established.

Which graph could represent the change in the rates of the forward and reverse reactions over

time?

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The decomposition of SO₃(g) is a dynamic equilibrium.

2SO₃(g) → 2SO₂(g) + O₂(g)

What happens when the pressure of the system is increased?

• The rate of reaction will decrease and the position of the equilibrium will move to the left.

• The rate of reaction will decrease and the position of the equilibrium will move to the right.

• The rate of reaction will increase and the position of the equilibrium will move to the left.

• The rate of reaction will increase and the position of the equilibrium will move to the right.

The Boltzmann distribution of molecular energies in a sample of aqueous hydrogen peroxide at

room temperature is shown.

Which diagram shows the Boltzmann distribution of molecular energies of aqueous hydrogen

peroxide maintained at room temperature when a catalyst, manganese(IV) oxide, is added?

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The diagram shows the Boltzmann distribution of molecular energies in one mole of a gas at two temperatures, T₁ and T₂.

Which statements are correct?

1 The shaded area represents the proportion of molecules with energies between E₁ and E₂ at temperature T₂.

2 No particles have zero energy at either temperature.

3 T₂ is a higher temperature than T₁.

• 1,2,3

• 1,2

• 2,3

• 1 only

Methanol, CH₃OH, can be produced industrially by reacting CO with H₂.

CO(g) + 2H₂(g)→ CH₃OH(g) H = –91 kJ mol^–1

The process can be carried out at 4 X 10³ kPa and 1150K.

Which statements about this reaction are correct?

1 Increasing the temperature will increase the rate of reaction because more effective collisions will occur.

2 Lowering the temperature will reduce the rate of reaction because the forward reaction is exothermic.

3 Increasing the pressure will reduce the rate of reaction because there are a larger number of moles on the left-hand side of the equation.

• 1,2,3

• 1,2

• 2,3

• 1 only

Ammonia is made by the Haber process. The reactants are nitrogen and hydrogen.

N₂(g) + 3H₂(g)→2NH₃(g) ∆H is negative

What will increase the rate of the forward reaction?

• adding argon to the mixture but keeping the total volume constant

• decreasing the temperature

• increasing the total pressure by reducing the total volume at constant temperature

• removing ammonia as it is made but keeping the total volume of the mixture the same

An autocatalytic reaction is a reaction in which one of the products catalyses the reaction.

Which curve would be obtained if the rate of an autocatalytic reaction is plotted against time?

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Which factors can lead to an increase in the rate of a reaction?

1 a lower activation energy

2 an increase in temperature

3 an increase in the concentration of a reactant

• 1,2,3

• 1,2

• 2,3

• 1 only

The diagram shows the Boltzmann energy distribution curves for molecules of a sample of a gas at two different temperatures.

Which letter on the axes represents the most probable energy for molecules of the same sample of gas at the lower temperature?

• A

• B

• C

• D